Conventionally, a Mach-Zehnder interferometer is sometimes used as an optical modulator connected to an optical fiber and for modulating light emitted from the optical fiber. In recent years, because an optical modulation method is diversified, the optical modulator often includes a plurality of Mach-Zehnder interferometers. In this case, by integrating the Mach-Zehnder interferometers on one chip, it is possible to reduce the size of the optical modulator.
In the optical modulator provided with the Mach-Zehnder interferometers, signal electrodes and ground electrodes are formed along parallel Mach-Zehnder type optical waveguides. For example, a radio frequency (RF) electrode for a high-frequency signal for superimposing data on light and a direct current (DC) electrode for a DC signal for controlling the phase of light are, in some cases, provided as signal electrodes in the optical modulator. Of these electrodes, the RF electrode is connected to an RF pin as a lead pin, and an RF signal being an electrical signal according to a data signal is input from the RF pin. The light emitted from the optical fiber is then modulated by the RF signal input to the RF electrode.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2010-217427
Patent Literature 2: Japanese Laid-open Patent Publication No. 2016-71199
An RF pin of an optical modulator and a driver that generates an RF signal according to a data signal may sometimes be connected to each other via, for example, flexible printed circuits (FPC). In other words, one end of the FPC on the driver side is electrically connected to a wiring pattern for outputting the RF signal sent from the driver, and one end of the FPC on the optical modulator side is accommodated in a cut-out portion formed in the optical modulator and is electrically connected to the RF pin protruding toward, for example, the cut-out portion. However, when the RF pin of the optical modulator and the driver are connected to each other via the FPC, the size of the optical modulator is increased along the direction in which the FPC extends, and the mounting area may be increased. Therefore, the connection using the FPC is not practical.
Therefore, it is conceivable that the driver is accommodated in the cut-out portion of the optical modulator and the driver and the optical modulator are connected in the cut-out portion by a connecting member other than the FPC, thereby reducing the mounting area corresponding to the driver and reducing the size of the device. For example, it is conceivable that a connector electrically connected to the RF electrode is embedded in the upper surface of the cut-out portion of the optical modulator, the driver is accommodated in the cut-out portion of the optical modulator so as to face the connector, and that the wiring pattern for outputting the RF signal from the driver and the connector are connected by coaxial pins. However, in this configuration, because the wiring for inputting the data signal to the driver reaches an input interface of the data signal by detouring the position opposite to the connector across the driver, detouring of the wiring makes it difficult to arrange other components in an arrangement space of the wiring. As a result, because this configuration requires another arrangement space for arranging other components, there is a problem that the mounting area is not effectively used.
In this way, in the configuration in which the driver is accommodated in the cut-out portion of the optical modulator, it is expected to achieve downsizing of the device by reducing the mounting area.